Development of multiplexing techniques has enabled concurrent combination of video data, audio data, and system information which are transmitted via a transport stream. Accordingly, digital data broadcasting has overcome the problems of conventional analog broadcasting and has provided multimedia services with high added value to service subscribers. For example, the Advanced Television Systems Committee (ATSC) standard is used in United States for transmitting TV programs to receivers through broadcasting wireless communication signals, and the Digital Video Broadcasting (DVB) standard is adopted in Europe for transmitting TV programs to receivers through broadcasting wireless communication signals.
In general, the TV program content providers desire their various broadcasted multimedia data to be protected and only provided to authenticated subscribers. The conditional access system is therefore developed in order to satisfy such requirements. The conditional access system is designed for controlling each receiver (e.g., a digital television set-top box) to determine whether to give a right to present a specific broadcasted TV program to a viewer. The conditional access system is based on the transmission of programs scrambled with control words which are received by subscribers having a set-top box and a PCMCIA-like card, such as a Point of Deployment (POD) card or a CableCARD for an ATSC receiver or a Common Interface (CI) for a DTV receiver, inserted to the set-top box. The PCMCIA-like card is to allow the scrambled programs transmitted via a broadcasting wireless communication signal to be descrambled and viewed.
With the development of the digital broadcasting, the specification associated with the conditional access system might be modified, which necessitates a new processing flow for the scrambled transport stream generated from a demodulator demodulating an input signal provided through a tuner. Therefore, how to design an apparatus compatible with the updated conditional access specification becomes an important issue for the designers.